When teeth have defects and the like, it is necessary to restore such defects. When defects and the like are to be restored, there are occasions where a cast crown restoration treatment, a defect prosthetic treatment or the like is needed. In this case, first, a mold having a negative form that replicates the shape of an abutment tooth, which has been subjected to a basic treatment or the like, is taken. Subsequently, by using the mold thus obtained, a cast of the abutment tooth or the like is produced using plaster or the like. Thereafter, a prosthesis is produced by utilizing the cast thus produced. Lastly, the prosthesis thus produced is installed on the abutment tooth or the like, and thereby the tooth is restored. This shape of an abutment tooth or the like is referred to as impression, and the curable material used to produce a solid mold that represents a specific shape by taking an impression is referred to as an impression material.
Generally, an alginate impression material, an agar impression material, a silicone rubber impression material, a polysulfide rubber impression material, a polyether rubber impression material, or the like is used as the impression material. Among these, an alginate impression material is most widely used because the material is inexpensive and easily handleable.
An alginate impression material includes a base material containing an alginic acid salt as a main component, and a curable material containing calcium sulfate as a main component. When the base material and the curable material are kneaded in the presence of water, a gel-like curable material is obtained. The alginate impression material is an impression material which utilizes the curing phenomenon described above.
The operation of taking an impression by using an alginate impression material (hereinafter, may be briefly described simply as “impression material”) is carried out by the following procedure. First, a base material and a curable material are kneaded, and thus an impression material prior to curing is obtained. Subsequently, this impression material prior to curing is loaded on an impression tray which has replicated the dentition. Thereafter, the tray loaded with the impression material is pressed against the teeth such that the teeth in the oral cavity are wrapped up by the impression material. Lastly, after the impression material cures, the impression material that has adhered to the tray and is integrated therewith is removed from the teeth, and the impression material is withdrawn from the oral cavity together with the tray.
The tray used to take an impression is roughly classified into two types: stock trays and custom trays. The stock trays are trays having ready-made sizes and shapes. Specific examples of the stock trays include trays made of metals such as stainless steel, brass, and brass provided with chrome plating. The custom trays are trays that are produced with separate shapes in accordance with different individuals. Specific examples of the custom tray include resin trays formed from polymethacrylic acid esters, and trays made of modeling compounds formed from thermoplastic resins. Meanwhile, as the polymethacrylic acid esters that serve as the material of resin trays, usually polymethyl methacrylate, polyethyl methacrylate, a methyl methacrylate-ethyl methacrylate copolymer, and the like are used.
Since alginate impression materials have low adhesiveness to the various trays described above, when an impression material is removed from the teeth, there are occasions in which the impression material is detached from the tray. When the impression material is detached from the tray, the shape of the impression taken is likely to change significantly. Therefore, when the impression material is detached, there is a problem that a highly accurate impression cannot be taken.
In order to address the problem described above, a method of using a reticulated tray, an undercut-shaped tray or a tray having punched holes, may be contemplated. When a tray having such a shape is used, the contact area between the tray and the impression material increases, and the holding power between the impression material and the tray is enhanced. As a result, the impression material is not easily detached from the tray.
On the other hand, in the case of using, not a tray having a shape such as described above, but a stock tray or custom tray which is plate-shaped with a smooth surface, it is necessary to increase the holding power between the impression material and the tray by any means.
Regarding a method of increasing the holding power, there is a method of increasing the holding power between a tray and an impression material by applying, between the two members, an adhesive containing a fine powder and an organic solvent (see Patent Document 1). As the solvent, resin-swellable organic solvents (for example, xylene, toluene and ethyl acetate) are used. The solubility parameters (δ) of these solvents are in the range of 17.0 to 20.5 [(MPa)1/2].
As another method, a method of bonding a tray and an impression material by using an adhesive containing a polyamine compound containing two or more amino groups in one molecule, a solvent, and suitably an organic peroxide (see Patent Document 2) is available.
In the adhesive disclosed in Patent Document 1, a resin-swellable organic solvent having a solubility parameter value which is within the range of solubility parameter described above, is used as the solvent. The action of this organic solvent is to swell and dissolve the surface of the tray, and to attach the fine powder component to the tray surface. The adhesive force between the tray and the impression material is a force that is increased only by the physical interlocking force between the fine powder component and the impression material. Therefore, in the case where the system depends on the increase of the adhesive force based on physical interlocking force as such, fluctuations in the adhesive force cannot be prevented from occurring. Furthermore, this adhesive is effective for a tray made of a resin or a tray made of a modeling compound, which are both swellable in the presence of an organic solvent. However, when the adhesive is used for a tray made of a metal, the adhesive force increasing effect is hardly recognized.
On the other hand, in the adhesive disclosed in Patent Document 2, crosslinking is formed between the amino groups carried by the polyamine compound and the carboxyl groups carried by the alginate impression material that are incorporated.
Furthermore, since the polyamine compound has high affinity with various tray materials, high adhesive force is exhibited not only with a tray made of a resin or a tray made of a modeling compound, but also with a tray made of a metal. As a result, the adhesive force between the various trays described above and impression materials is fairly high.
However, the adhesive force between a tray and an impression material exhibited by the aforementioned adhesive is still not satisfactory for the purpose of practical use, and there is room for further improvement.
Particularly, in the case of bonding an impression material to a resin tray by using this adhesive, and taking an impression in the oral cavity, it was found that if the contact pressure to press the impression material loaded on the tray against the teeth is insufficient, the adhesive force between the tray and the impression material decreases. Specifically, an area where a relatively high contact pressure (100 gf/cm2 or greater) is exerted, such as a site where the teeth collide with the tray, is satisfactorily bonded. However, at an area where a relatively weak contact pressure (20 gf/cm2 or less) is exerted, such as the rim of the tray, the adhesive force decreases.
On the other hand, in order to increase the adhesive force between the tray and the impression material, a method of increasing the surface roughness of the tray made of a resin is available. As a method of increasing the surface roughness, a method of subjecting the tray surface to a polishing treatment (grinding the surface using a dental turbine or the like) or to a sand blast treatment, may be used. In the case of a tray with high surface roughness (usually, in terms of the value (Ra) measured with a contact type surface roughness meter according to JIS B 0601, a tray having a surface roughness of greater than 1.0 μm), an alginate impression material can be bonded to the tray with high adhesive force by using the adhesive described above. However, in the case of a resin tray which has not been subjected to such a treatment (having a surface that has not be roughened) (the surface roughness (Ra) is 1.0 μm or less), the tray and the impression material cannot be bonded with sufficient strength even if the aforementioned adhesive is used.
Under such circumstances, the inventors of the present invention conducted an investigation to use, in this adhesive of Patent Document 2, a resin-swellable organic solvent having a solubility parameter value in the range described above in particular as a solvent, and further to incorporate inorganic particles having an average particle size of 10 μm or less. As a result, the inventors found that this adhesive exhibits a markedly increased adhesive force against a tray made of a resin, and previously proposed the adhesive (see Patent Document 3). That is, in the case of using a tray made of a resin, even if the contact pressure against the teeth and the like is week, or even if a tray having a smooth surface that has not been polished is used, the tray and the impression material are strongly bonded using the improved adhesive as described above.    Patent Document 1: Japanese Patent No. 3778731    Patent Document 2: International Application WO 2008/105452    Patent Document 3: Japanese Patent Application Laid-Open No. 2010-57905